Scientists published results of a study that indicated that a doubling of carbon dioxide in the atmosphere could raise the temperature of the Earth’s atmosphere and lead to widespread environmental disaster. Later research has predicted that unchecked global warming could lead to the complete destruction of life on Earth.
In May, 1967, Syukuro Manabe and Richard Wetherald published an article in the Journal of the Atmospheric Studies describing results of computations related to greenhouse, or global, warming. These results incorporated an assumption of constant relative humidity, a more realistic assumption than one previously used of constant absolute humidity.
Manabe and Wetherald concluded that global atmospheric temperatures were much more sensitive to carbon dioxide (CO2) content, ozone content, cloudiness, and variations in the solar constant than previous models had indicated. In particular, their model predicted an increase of about 2 degrees Celsius for the average temperature of the atmosphere if its CO2 content were doubled. This paper also provided some of the theoretical foundation required for much more complex general circulation models (GCMs). Many of these have since been developed and are key tools in efforts to predict future climatic conditions.
The concept of greenhouse warming, or the greenhouse effect, can be understood by considering what happens inside a car parked in the sun. The glass of the windshield and the windows is transparent to sunlight, which enters easily and then warms the interior surfaces of the car. As these surfaces warm, they heat the air in the car. If the windows are closed, this warm air cannot escape, and the interior of the car gets hotter and hotter. The glass windows do not let the heat (long wavelength radiation) out as easily as they let the sunlight (short wavelength radiation) in. Heat, however, is conducted through the glass. Otherwise, the temperature inside the car would continue to climb without limit.
Heat (measured in calories) is conducted from inside the car to outside the car at a rate that depends on the temperature difference between inside and outside the car. The temperature (measured in degrees) inside the car will continue to rise as long as the solar energy (measured in calories) coming in through the windows is greater than the heat leaving the car. A point will be reached at which the temperature difference inside and outside the car is great enough for the rate of heat conduction to equal the incoming solar energy, and that will be the equilibrium temperature for the car. With an outside temperature below freezing, a large temperature difference between inside and outside can be established without the inside temperatures becoming uncomfortably warm. This is not the case when the outside temperatures are high.
With the increase in “greenhouse gases” such as carbon monoxide in Earth’s atmosphere, the Sun’s heat becomes trapped (straight arrows), leaving less to escape back into space (wavy arrows); as a result, the overall temperature of the planet rises.
The role of greenhouse gases is similar to the role of glass in this example. Adding CO2 or other greenhouse gases to the atmosphere is like making car windows thicker. These gases make it more difficult for heat to move through the atmosphere, which means that a larger temperature difference between the surface of the earth and outer space is required to get the heat to move across it and escape as fast as solar energy is coming in. Because the temperature of outer space is always near absolute zero, the only way this can occur is for the temperature near the surface of the earth to increase.
Greenhouse gases move as part of the atmosphere and some, particularly water vapor, can move in and out of the atmosphere. Heat is transferred through the glass in a car window by conduction; it moves through the atmosphere by convection and radiation. The concept is similar, but the physics is considerably more complex. This is the problem Manabe and Wetherald were working on. Their 1967 paper presented work that was the next step in a series of studies of the equilibrium state of the atmosphere.
Carbon dioxide is produced inside the human body by the very metabolic processes that sustain life. CO2 is exhaled from the lungs into the atmosphere, where it joins the CO2 produced by the respiration of most other forms of life on the planet. It is inserted under pressure in carbonated beverages and is used in its solid form, dry ice, to keep things cold. CO2 constitutes less than 0.04 percent of the earth’s atmosphere, does not appear to cause illness, and is colorless and odorless. CO2 was not considered a pollutant before 1967.
Manabe and Wetherald showed that CO2 in the atmosphere might influence global temperatures and that the effect was greater than many people had previously thought. At the same time, data from the CO2 observatory established in 1958 on Mauna Loa during the International Geophysical Year
The increase in CO2 is a result of the burning of fossil fuels, deforestation, cement production, agricultural processes, and other anthropogenic activities. Scientists have estimated the amounts of CO2 being produced by these activities and have compared their findings with the rate of increase in CO2 in the atmosphere. They found that only about one-half of the anthropogenic CO2 produced each year is accumulating in the atmosphere; the rest of it may be going into the oceans or increased biomass. The unaccounted-for CO2 is the subject of considerable current research. The fact that no one knows where half of the anthropogenic CO2 is going raises questions in some minds about the reliability of much of the work involving the carbon cycle. The rate at which CO2 was accumulating in the atmosphere in the late twentieth century was expected to cause it to double from the 1967 levels sometime in the twenty-first century.
Research continues into the effect of global warming on the planet and its inhabitants. Melting ice could raise sea levels, productive farmland could become desert, and natural vegetation patterns could change. People could be driven from coastal areas and heating costs could go down, but cooling costs would rise. Most predictions have painted a bleak picture, suggesting that global warming would be a calamity. Mitigating global warming involves curtailing the use of fossil fuels, ending deforestation in the tropics, and controlling population growth, among other things.
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Bily, Cynthia A., ed. Global Warming. San Diego, Calif.: Greenhaven Press, 2006. Part of the Opposing Viewpoints series. Essays debate global warming and its causes and effects. -
Dickinson, Robert E. “Use of Numerical Models to Project Greenhouse Gas-Induced Warming in Polar Regions (the Conceptual Basis Developed over the Last Twenty Years).” In Ozone Depletion, Greenhouse Gases, and Climate Change, edited by the National Research Council. Washington, D.C.: National Academy Press, 1989. Provides an update on the state of climate modeling. Describes many of the complexities ignored in early models such as ice and cloud cover and seasonal variations. -
Drake, Frances. Global Warming: The Science of Climate Change. New York: Oxford University Press, 2000. Chapters in this practical study of climates and climate change include “Basic Physical Concepts,” “The Climate System,” “Past Greenhouses and Icehouses,” “Historical Climate Change,” “The Observational Evidence for Global Warming,” and “The Model Evidence for Global Warming.” -
Gore, Al. An Inconvenient Truth: The Planetary Emergency of Global Warming and What We Can Do About It. Emmaus, Pa.: Rodale Press, 2006. Former U.S. vice president Al Gore traces global warming, focusing on its urgency and its denial by world leaders. -
Houghton, Richard A., and George M. Woodwell. “Global Climatic Change.” Scientific American, April, 1989, 36-44. Argues that CO2-induced global warming has begun and gives several grim scenarios on how it will continue, with largely negative results for most. -
Kellogg, William W., and Robert Schware. Climate Change and Society: Consequences of Increasing Atmospheric Carbon Dioxide. Boulder, Colo.: Westview Press, 1981. Abundant bibliographies, maps, and figures augment this carefully written review of global warming. Provides a summary of many general circulation models published through 1980. -
Reay, David. Climate Change Begins at Home: Life on the Two-way Street of Global Warming. New York: Macmillan, 2005. Written especially for general readers, this book treats global warming as a problem that can be mitigated by changing one’s everyday habits of consumption and use. -
Revelle, Roger. “Carbon Dioxide and World Climate.” Scientific American, August, 1982, 35-43. A reasonable appraisal of most aspects of the CO2-induced global warming question. Thorough and easy to read. -
U.S. Congress. Senate. Committee on Governmental Affairs. Carbon Dioxide Accumulations in the Atmosphere, Synthetic Fuels, and Energy Policy: A Symposium. Washington, D.C.: Government Printing Office, 1979. Testimony and supporting materials presented to a Senate subcommittee investigating CO2-induced global warming. Intended for nonscientists, the material presented here is easily understood. Fascinating reading. Supporting material comes from a variety of sources and includes numerous figures, graphs, and charts. -
Weller, Gunter D., et al. “Detection and Monitoring of CO2-Induced Climate Changes.” In Changing Climate: Report of the Carbon Dioxide Assessment Committee, edited by the National Research Council. Washington, D.C.: National Academy Press, 1983. Organized around a government outline, this chapter points out many variables other than CO2, such as solar constant variations and volcanoes, which may change global temperatures. Outlines techniques and measurements that could be used to establish the extent of CO2’s contribution to global warming trends.
Lindeman’s “The Trophic-Dynamic Aspect of Ecology” Is Published
Osborn Publishes Our Plundered Planet
Congress Passes the Air Pollution Control Act
Mumford Warns of the Dangers of Growing Cities
Antarctic Treaty Goes into Force
Bookchin Warns of Health Hazards of Artificial Environments
Clean Air Act Grants Federal Authority to Regulate Air Pollution
Congress Passes the Motor Vehicle Air Pollution Control Act
First Earth Day Is Celebrated
Congress Amends the Clean Air Act